1. Field of the Invention
The present invention relates to electric fans and more particularly to a brushless fan motor control circuit assembly, which controls the operation of the motor of the electric fan accurately and safely, avoiding fan vibration.
2. Description of the Related Art
A conventional brushless motor for electric fan is a low voltage motor that must be used with a power control switch and has drawbacks of big size and high manufacturing cost. Further, a conventional brushless motor has no means to limit the current, to suppress high frequency noises or to enhance the power factor, i.e., low power factor results in waste of power. When a high voltage motor is used with the controller thereof directly connected to city power supply, the field effect transistor (MOS tube) may burn out upon a short circuit or phase lack. Further, the speed control of a brushless motor is done by means of pulse wave modulation (PWM), i.e. by means of pulse duty ratio to regulate the speed. When at a low speed, giving a high voltage repulsing pulse, the rotor is pushed to a next magnetic pole, and then attracted by this next magnetic pole. For controlling the speed, it occupies (stops) a time space so that the controller can change the phase (change the magnetic field), however, repulsion pushes to a next magnetic pole causes magnetic field exchange speed to be high at one time and low at another, and at this time, the fan will vibrate and cause noises.